Date: Mon, 27 Feb 2023 22:12:19 GMT From: Warner Losh <imp@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: fd88f4e190bc - main - pps: Simplify capture and event processing Message-ID: <202302272212.31RMCJx0028799@gitrepo.freebsd.org>
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The branch main has been updated by imp: URL: https://cgit.FreeBSD.org/src/commit/?id=fd88f4e190bc0a56f8d30179900553ce12d1c0d7 commit fd88f4e190bc0a56f8d30179900553ce12d1c0d7 Author: Sebastian Huber <sebastian.huber@embedded-brains.de> AuthorDate: 2023-02-27 21:49:09 +0000 Commit: Warner Losh <imp@FreeBSD.org> CommitDate: 2023-02-27 22:10:55 +0000 pps: Simplify capture and event processing Use local variables for the captured timehand and timecounter in pps_event(). This fixes a potential issue in the nsec preparation for hardpps(). Here the timecounter was accessed through the captured timehand after the generation was checked. Make a snapshot of the relevent timehand values early in pps_event(). Check the timehand generation only once during the capture and event processing. Use atomic_thread_fence_acq() similar to the other readers. Reviewed by: imp Pull Request: https://github.com/freebsd/freebsd-src/pull/604 --- sys/kern/kern_tc.c | 38 ++++++++++++++++++++------------------ 1 file changed, 20 insertions(+), 18 deletions(-) diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c index 20520adc0aba..b466fd4399e4 100644 --- a/sys/kern/kern_tc.c +++ b/sys/kern/kern_tc.c @@ -1772,14 +1772,14 @@ pps_capture(struct pps_state *pps) #endif tc = th->th_counter; pps->capcount = tc->tc_get_timecount(tc); - atomic_thread_fence_acq(); - if (pps->capgen != th->th_generation) - pps->capgen = 0; } void pps_event(struct pps_state *pps, int event) { + struct timehands *capth; + struct timecounter *captc; + uint64_t capth_scale; struct bintime bt; struct timespec ts, *tsp, *osp; u_int tcount, *pcount; @@ -1798,9 +1798,17 @@ pps_event(struct pps_state *pps, int event) /* Nothing to do if not currently set to capture this event type. */ if ((event & pps->ppsparam.mode) == 0) return; + + /* Make a snapshot of the captured timehand */ + capth = pps->capth; + captc = capth->th_counter; + capth_scale = capth->th_scale; + tcount = capth->th_offset_count; + bt = capth->th_bintime; + /* If the timecounter was wound up underneath us, bail out. */ - if (pps->capgen == 0 || pps->capgen != - atomic_load_acq_int(&pps->capth->th_generation)) + atomic_thread_fence_acq(); + if (pps->capgen == 0 || pps->capgen != capth->th_generation) return; /* Things would be easier with arrays. */ @@ -1838,25 +1846,19 @@ pps_event(struct pps_state *pps, int event) * If the timecounter changed, we cannot compare the count values, so * we have to drop the rest of the PPS-stuff until the next event. */ - if (pps->ppstc != pps->capth->th_counter) { - pps->ppstc = pps->capth->th_counter; + if (__predict_false(pps->ppstc != captc)) { + pps->ppstc = captc; *pcount = pps->capcount; pps->ppscount[2] = pps->capcount; return; } /* Convert the count to a timespec. */ - tcount = pps->capcount - pps->capth->th_offset_count; - tcount &= pps->capth->th_counter->tc_counter_mask; - bt = pps->capth->th_bintime; - bintime_addx(&bt, pps->capth->th_scale * tcount); + tcount = pps->capcount - tcount; + tcount &= captc->tc_counter_mask; + bintime_addx(&bt, capth_scale * tcount); bintime2timespec(&bt, &ts); - /* If the timecounter was wound up underneath us, bail out. */ - atomic_thread_fence_acq(); - if (pps->capgen != pps->capth->th_generation) - return; - *pcount = pps->capcount; (*pseq)++; *tsp = ts; @@ -1890,9 +1892,9 @@ pps_event(struct pps_state *pps, int event) */ tcount = pps->capcount - pps->ppscount[2]; pps->ppscount[2] = pps->capcount; - tcount &= pps->capth->th_counter->tc_counter_mask; + tcount &= captc->tc_counter_mask; scale = (uint64_t)1 << 63; - scale /= pps->capth->th_counter->tc_frequency; + scale /= captc->tc_frequency; scale *= 2; bt.sec = 0; bt.frac = 0;
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